In the paper it is shown that the technical-constructive elements which brin about the productivity of a portal crane, used in the forrestry sector, operate by the means of three speed of translation (that of the crane, the trollez and the grab) and are represented, for each of the speeds bz the revolutions of the actuating motor, the transmission ratio and the diameter of the last element belonging to the transmission kinematic chain. For exemplification of the actual way in which operate the above mentioned elements, the necessary measurements for determining the hourly productivity for two protal cranes of similar construction (and in the same running conditions), but with some differences, especialy regarding the transmission ratio from electromotor to the grab and the diametere of the last element belonging to the ansmission kinematic chain were carried out. It was proved, finally, that the crane model M.P.8.b.32+15+15 (B) where the transmission ratio is lower and the drum diameter on which it wraps up the grab manoeuvring cable is higher, achieves a higher hourly productivity compared to another model of crane (M.P.8.b.32, 5+15+14,0 - (A). The variation of the productivity with the lenght of the crane translation lay-out is non linear having the shape of a decresing exponential curve. The difference between the hourly productivity of the two models of crane is dimishing as the translation lay-out increases.
Keywords: cranes, wood industrialisation, productivity